Methods of and baths for electrodepositing cobalt or cobalt-molybdenum alloys



Patented Sept. 22, 1953 METHODS OF AND BATHS FOR ELEC- TRODEPOSITING COBALT OR COBALT- MOLYBDENUM ALLOYS Abner Brenner, Chevy Chase, Md., and Polly Burkhead, Bethlehem, Pa., assignors to the United States of America as represented by the Secretary of War No Drawing. Application November 8, 1946, Serial No. 708,565

(Granted under Title 35, U. S. Code (1952),

11 Claims.

sec. 266) l The invention described in the following specification and claims may be manufactured and used by or for the United States Government for govermnental purposes without the payment to us of any royalty thereon.

This invention relates to the use of carbonate baths in the electrodeposition of metals, and it has particular reference to the use of such baths for the electrodeposition of cobalt or alloys of cobalt and'molybdenum.

Broadly stated the object of our invention is to utilize solutions of carbonate salts as electroplating baths.

A more specific object is to provide a method for improving the electrodeposition of cobalt.

Another object is to provide a method for satisfactorily electrodepositing alloys of cobalt and molybdenum.

A further object is to provide a method and n means for obtaining a metallic deposit which is extremely hard, highly resistant to corrosion, and possesses a surface that is highly durable under high temperature conditions.

A still further object is to achieve the foregoing with maximum economy and current efficiency.

One more object is to provide a relatively inexpensive and stable bath for the electrodeposition of cobalt and cobalt-molybdenum alloys that is comparatively simple to prepare and operate.

We have discovered that certain complex carbonate solutions make excellent plating baths, a fact which apparently has never before been known or utilized in the prior art. Such baths have been found particularly advantageous in the plating of cobalt or of cobalt-molybdenum alloys.

With reference to the electrodeposition of cobalt alone, it has long been known that cobalt salts will dissolve in strong solutions of sodium or potassium carbonate and also in solutions of the bicarbonates. bility of the complex cobalt compounds is not very high. It has been found, however, that upon heating the complex carbonate solutions, the solubility for cobalt is increased. This heating does not affect the character of the complex carbonate solutions for they are quite stable to heat, although they do precipitate on dilution or on being made more alkaline with caustic soda or potash. Thus, it is important, in practicing our invention, to avoid dilution of the carbonate bath and to keep it free of caustic.

The excellent deposits of cobalt which We have been able to achieve with our novel bath of complex carbonates have been found to be excep- On the other hand, the solutionally good when the bath is heated to 100 C. or even to the boiling point. Although such higher temperatures are preferable when practicing our invention, they are not essential thereto for cobalt will deposit from the carbonate bath even at room temperatures.

As a typical example of our unique carbonate electrolytic bath we may cite the following com-' position which was one of many formulations which our experiments have shown to enable the successful practice of our invention. These formulations difier one from another in their con stituents and in variations of concentration. The bath we have in mind contains approximately 1300 grams per liter of potassium carbonate, and 10 grams per liter of cobalt which may be in the form of the sulfate or chloride salt.

It should be understood that still other sources of cobalt and of carbonates may be employed either singly or in combination. For example, cobalt acetate, hydroxide or freshly precipitated carbonate may be utilized. The carbonate of sodium may be substituted for potassium carbon- Iate although the latter salt is preferable because it is more soluble than the former.

In operating our improved electrolytic bath, we have found that deposits of cobalt may be obtained at current densities ranging from 1 to 5 amperes per square decimeter (hereinafter represented as amp./dm. It has been our observation that when such relatively low current densities are employed the cobalt deposit which results is quite smooth, Whereas the effect of using higher current densities is'to make the resulting deposit rather rough. When the bath is operated at the elevated temperatures above described, the cathode current efficiency has been noted to be about 100%.

In addition to our above described improved method for plating cobalt, and the superior product which that method makes possible, our invention has provided for the first time in the art a method for successfully electroplating alloys of cobalt and molybdenum. In practicing this invention we also utilize a carbonate bath. As a matter of fact, we can preferably employ the above described cobalt carbonate bath which furnishes a good base for the co-deposition of the two alloying metals as will now be described.

The baths which we used in plating cobaltmolybdenum alloys contained various concentrations of potassium carbonate ranging from several hundred grams per liter up to the saturation point; for example, from 600 up to 1500 grams per liter, the higher concentrations being a: preferable. The cobalt concentration also may be varied from a few grams per liter up to saturation, as for example, from to 20 grams per liter. Here, too, higher concentrations are to be preferred.

The baths molybdenum v constituent is furnished in the form of sodium molybdate, potassium molybdate, molybdic oxide or any other soluble salt of molybdenum with the exception of the ammonium salt (Which'has a detrimental affect on the plating result) The quantity of molybdenum salt may range from several grams per liter up to saturation depending on the composition of deposit required. A typical bath composition, one of many which we have found suitable for practicing our invention, contains about 1,000 grams per liter of potassium carbonate, approximately 15 grams per liter of cobalt added in the form of the sulfate or chloride salt, and 100 grams per liter of sodium molybdate. The pH of this bath is 11.

We have found that a preferred range of temperature within which this bath should be operated is from approximately 90 C. to about 135 (3., although successful results may be obtained when the plating is carried on at room temperature up to the baths boiling point, which is about 135 C.

As in the case where just cobalt alone is being electroplated, the best deposits of the cobaltmolybdenum alloys are obtained at elevated temperatures, as the deposits tend to contain oxides when plated out at the lower temperatures. We have observed that the deposits from a given bath contain less molybdenum when plated at the recommended elevated temperatures, but we find this practice desirable because the resulting deposits are much more sound than those which are obtained at low plating temperatures.

The just described operation may preferably be carried out by employing a current density of deposition varying from 1 to .5 amp./dm. with best results being obtained at the lower values. With this procedure, the cathode current efficiency has been noted to vary from 20 to 100%, the higher efiiciencies being obtained at the elevated temperatures.

We have further found that the practice of our unique alloy plating invention may be further enhanced by the use of either cobalt or molybdenum anodes. The molybdenum anodes corrode with good current efilciency as long as the current density does not get too high. Forex ample, a current density of 5 amp./dm. is satisfactory, but 20 amp/dim. is too high. Tungsten may also be used as anode material, since it dissolves anodically with good efficiency and does not co-deposit (with the cobalt and molybdenum) from the carbonate bath.

The products which have been plated with alloys of cobalt-molybdenum produced in accordance with our novel method hereinbefore described have been given numerous laboratory and practical tests which have demonstrated that the electrodeposited alloy is very hard, highly resistant to corrosion, and possesses a surface which is very durable under extremely high temperature conditions.

The foregoing has made clear the manner in which the objects for our invention, as set forth at the outset of this specification, have been accomplished. Thus, it will be seen that we have utilized solutions of carbonate salts as electroplating baths; that we have provided a method for improving the electrodeposition of cobalt;

that we have provided a method for satisfactorily electrodepositing alloys of cobalt and molybdenum; that we have provided means for obtaining a metallic deposit which is extremely hard, highly resistant to corrosion, and possesses a high durable surface under high temperature conditions; that we have achieved the foregoing with maximum current efficiency and economy; and that we have provided a relatively inexpensive and stable bath for the electrodeposition of cobalt and cobalt-molybdenum alloys that is comparatively simple to prepare and operate.

As we previously indicated, certain variations of :bath composition, types of anodes, etc., from the specific instances here given by way of illustration may be resorted to without departing from the spirit and scope of our invention. However, it is quite conceivable, and it will be readily understandable to those skilled in the art, that such carbonate baths may be used for electroplating numerous other metals with but relatively minor changes to the constituents and operation steps necessary to the practice of our invention.

Our invention is therefore extensive in its adaptation and is not to be restricted to the particular forms here described by way of illustration.

We claim:

1. As a bath for the electrolytic deposition of cobalt, a caustic-free, strongly alkaline solution which essentially contains a carbonate salt plus a surhcient amount of a soluble cobalt salt to provide the ions necessary to the formation of a desired electrodeposited coating of cobalt.

2. As a bath for the electrolytic deposition of cobalt, a caustic-free, strongly alkaline solution containing approximately 1300 grams per liter of potassium carbonate and a sufiicient amount of cobalt chloride which will supply approximately 10 grams per liter of cobalt to said bath.

3. As a bath for the electrolytic deposition of cobalt, a causticfree, strongly alkaline solution containing approximately 1300 grams per liter of potassium carbonate and a sufficient amount of cobalt sulfate which will supply approximately 10 grams per liter of cobalt to said bath.

4. As a bath for the electrolytic co-deposition of cobalt and molybdenum, a caustic-free, strongly alkaline solution which essentially contains a carbonate salt plus sufiicient amounts of a soluble cobalt salt and a soluble molybdenum salt to provide the ions of each metal necessary to the formation of a desired electrodeposited coating of cobalt-molybdenum alloy.

5. As a bath for the electrolytic co-deposition of cobalt and molybdenum, a caustic-free, strongly alkaline solution containing approximately 1000 grams per liter of potassium carbonate, a sufiicient amount of cobalt chloride which will supply approximately 15 grams per liter of cobalt to said bath, and grams per liter of sodium molybdate.

6. As a bath for the electrolytic co-deposition of cobalt and molybdenum, a caustic-free, strongly alkaline solution containing approximately 1000 grams per liter of potassium carbonate, a sufficient amount of cobalt sulfate which will supply approximately 15 grams per liter of cobalt to said bath, and 100 grams per liter of sodium molybdate.

7. The method of electrodepositing cobalt which comprises passing electric current having a current density of from 1 to 5 amperes per square decimeter through a caustic-free, strongly alkaline bath containing a solution having a highly preponderant amount of a carbonate salt and a suflicient amount of a soluble cobalt salt to provide the ions necessary to the formation of a desired electrodeposited coating of cobalt.

8. The method of electrolytically co-depositing cobalt and molybdenum which comprises passing electric current having a current density of from 1 to 5 amperes per square decimeter through a caustic-free, strongly alkaline bath containing a solution having a highly preponderant amount of a carbonate salt and sufficient, amounts of a soluble cobalt salt and a soluble molybdenum salt to provide the ions of each metal necessary to the formation of a desired electrodeposited coating of cobalt-molybdenum alloy.

9. The method of electrodepositing cobalt which comprises passing electric current having a current density of from 1 to 5 amperes per square decimeter through a caustic-free, strongly alkaline bath containing a solution having a highly preponderant amount of a carbonate salt and a sufficient amount of a soluble cobalt salt to provide the ions necessary to the formation of a desired electrodeposited coating of cobalt, and heating the said bath to a temperature ranging from 100 C. to its boiling point.

10. The method of electrolytically co-depositing cobalt and molybdenum which comprises passing electric current having a current density of from 1 to 5 amperes per square decimeter through a caustic-free, strongly alkaline bath containing a solution having a highly preponderant amount of a carbonate salt and sufficient amounts of a soluble cobalt salt and a soluble molybdenum salt to provide the ions of each metal necessary to the formation of a desired electrodeposited coating of cobalt-molybdenum alloy, and heating the said bath to a temperature ranging from C. to its boiling point.

11. As a bath for the electrolytic deposition of a metallic material selected from the group consisting of cobalt and cobalt-molybdenum alloy, a caustic-free, strongly alkaline solution which essentially contains a carbonate salt plus a sumcient amount of a soluble material selected from the group consisting of soluble cobalt salts and soluble mixed cobalt-molybdenum salts to provide the ions necessary to the formation of a desired electrodeposited coating of the selected metallic material.

ABNER BRENNER. POLLY BURKHEAD.

References Cited in the file of this patent UNITED STATES PATENTS Number Name Date 1,344,869 Cutten June 29, 1920 2,428,404 Yntema Oct. 7, 1947 FOREIGN PATENTS Number Country Date 668,800 France July 22, 1929 

11. AS A BATH FOR THE ELECTROLYTIC DEPOSITION OF A METALLIC MATERIAL SELECTED FROM THE GROUP CONSISTING OF COBALT AND COBALT-MOLYBDENUM ALLOY, A CAUSTIC-FREE, STRONGLY ALKALINE SOLUTION WHICH ESSENTIALLY CONTAINS A CARBONATE SALT PLUS A SUFFICIENT AMOUNT OF A SOLUBLE MATERIAL SELECTED FROM THE GROUP CONSISTING OF SOLUBLE COBALT SALTS AND SOLUBLE MIXED COBALT-MOLYBDENUM SALTS TO PROVIDE THE IONS NECESSARY TO THE FORMATION OF A DESIRED ELECTRODEPOSITED COATING OF THE SELECTED METALLIC MATERIAL. 